The present invention relates to video measurements, and more particularly to a method of generating an MPEG (Moving Picture Experts Group) encoded signal for component analog video (CAV) measurement of linearity, channel delay, cross-talk and short time distortion.
A test signal for measuring component analog video, such as Y,Pb,Pr or RGB component video, has to solve the following problems:                for each measurement one line for all three component channels        valid in both RGB and YPbPr: ramps, sweeps, pulse and bar, etc.        digital RGB cross-talk due to aliasing of Cb and Cr in 4:0:0 to 4:4:4 formats        EAV (end active video) and SAV (start active video) meet specifications even with missing samples        macro-block boundaries        
A corresponding encoder/decoder has to solve the following problems:                remove vertical pre-filter        remove vertical post-filter        alter quantization tables alternate scanning for vertical boundary        motion estimation turned off.        
The prior art is represented by the Tektronix VM5000HD Signal Set which modifies a test signal to solve the following problems:                for each measurement one line for all three component channels        valid in both RGB and YPbPr for ramps and sweeps        digital RGB cross-talk due to aliasing of Cb and Dr in 4:0:0 to 4:4:4 standards        EAV and SAV meet specification even with missing samples        macro-block boundaries        
However a “standard” decoder is used. Although there is no “standard” for encoding, the term here refers to the fact that an encoder is designed for general purpose encoding with no optimization for test signals for component analog video.
FIG. 1 illustrates an ideal overlay of RGB component analog test signals that have a sweep signal at a specific location within each video line. If displayed on a video monitor, a portion of several lines of the image for one of the components shown in FIG. 1, i.e., horizontally one-third of the image lines, appears as shown in FIG. 2 with frequency increasing from left to right. Each of the components would appear the same, and would follow on the same image lines so that, when combined, the pattern of FIG. 2 is repeated three times horizontally across the image. FIG. 3 shows a GBR parade view of one video line for each of the component waveforms after MPEG coding/decoding of the component analog test signals of FIG. 1. As may be seen from FIG. 3 there is extraneous signal content in the portion of the G″ waveform that corresponds in location to the bursts for the B″ and R″ components. It is readily apparent that there is considerable cross-talk of blue into the green and red components, as well as to a lesser extent cross-talk from the green and red components into the blue component and green into the red component. This cross-talk is a result of the MPEG compression process, especially the conversion of 4:4:4 (RGB) video to 4:2:0 (chroma subsampled) video. The waveforms of the different component bursts vary as a result of the cross-talk also.
What is desired is a method of generating a single MPEG encoded sequence for multiple CAV measurements that solves all of the above-identified problems.